Conventionally, in order to visualize latent image generated on the photoreceptor of an electronic photographic copying apparatus through dry development (where the photoreceptor is provided with photoreceptive layer composed of inorganic or organic photoconductive material), a variety of powder toners containing coloring agents and bonding resin are widely used.
When executing the electronic photography, static latent image generated on the photoreceptor by applying charge and light-exposure is developed by the toner. The toner image generated in correspondence with the static latent image is transferred onto the copying paper, and then, toner image is fixed to the copying paper via the fixation roller like a heated roller or a pressurized roller for example, whereby the static latent image is visualized. After transferring the toner image onto a copying paper, residual toner is scraped off from the surface of the photoreceptor with a cleaning blade.
Recently, from the viewpoint of high sensitivity in the visual-ray region, surpassing durability and wear-resistance, and satisfactory compatibility with high-speed copying operation, application of a photoreceptor having a photoreceptive layer composed of amorphous silicon is proposed. The superficial potential of the proposed amorphous silicon photoreceptor is largely dependent on the thickness of the photoreceptive layer. If the layer thickness were strengthened for increasing the superficial potential, crystals significantly grow. This in turn degrades the uniformity of the surface of the photoreceptor itself. To prevent this, normally, the amorphous silicon photoreceptor is provided with 5 through 60 micrometers of the photoreceptive layer thickness for example within a scope that can preserve the uniformity of the surface of the photoreceptor without degradation. Nevertheless, even though the layer thickness were strengthened, the photoreceptive layer may easily generates uneven portion like pin holes, and yet, since the surface of the amorphous silicon photoreceptor bears low potential, the surface is adversely affected by environmental moisture. To eliminate those disadvantages, Japanese patent application Laid-Open No. 61-284771 (1986) proposes a toner for use with the amorphous silicon photoreceptor having low superficial potential, where the proposed toner has 50.degree. through 70.degree. C. of the glass-transferrable temperature and contains special polyester resin which absorbs less volume of moisture.
The proposed toner surpasses others in the moisture resistance and resistance against friction charge. However, in order to use the photoreceptor in specific regions where the toner characteristic remains stable, if the proposed toner were applied to the amorphous silicon photoreceptor having increased layer thickness, since the surface of the amorphous silicon photoreceptor is uneven, toner fuses itself with the photoreceptor and gradually grows itself, and finally, "toner filming" symptom will occur. More particularly, adhesion between the photoreceptor and the toner is largely dependent on the Coulomb's force generated by the superficial potential of static latent image on the photoreceptor and the amount of charge borne by the toner itself. The magnitude of the adhesion of amorphous silicon photoreceptor having low superficial potential is mainly dependent on the amount of charge borne by the toner. Accordingly, if the cleaning operations with residual-toner-scraping blade were repeatedly performed against image-generating apparatus using electronic photography, pressure generated by the blade and the friction heat between the surface of the photoreceptor and the blade adversely affect the toner adhered to the photoreceptor by the influence of the Coulomb's force. Furthermore, due to uneven surface of the amorphous silicon photoreceptor and sizable amount of charge borne by the toner, compatibility of the toner with the cleaning is lowered. As a result, the toner is fused to the photoreceptor, thus easily generating filming symptom. This not only results in the short service life of the toner and developing agent, but it also causes the toner to generate black spots and streaks of the toner on the copied image, thus significantly degrading the quality of the reproduced image. Furthermore, since the superficial potential of the amorphous silicon photoreceptor is very low, unstable image is easily generated in the solid portion of the copied image, and as a result, distinct and vivid image can hardly be reproduced on copying papers.
Independent of the proposed toner cited above, in order to promote compatibility of the toner with cleaning process, Japanese patent application Laid-Open No. 61-278861 (1986) proposes a toner for use with the amorphous silicon photoreceptor, where the toner containing polyester resin is added with fine powder of titanic-acid strontium. According to the proposed toner, compatibility with cleaning process can be promoted. However, any of those toners containing resin other than polyester resin is not fully compatible with cleaning process.
Due to satisfactory durability and wear-resistance, amorphous silicon photoreceptor is widely used for a large number of high-speed electrophotographic copying apparatuses, and thus, in addition to the durability against cleaning, quick fixation is also required for amorphous silicon photoreceptors. Accordingly, it is essential for the toner to quickly dissolve itself under low temperature in order that it can securely permeate and fix itself onto copying papers, and yet, dissolved toner should properly agglomerate and maintain satisfactory fixation characteristic without migrating itself onto the fixation roller.